Multifilament silk yarns are made of naturally produced silk. Most, if not all, medical applications of silk multifilament yarn of the prior art have been directed to the production of silk surgical sutures using raw silk multifilament yarn after degumming and often dyeing with black logwood dye. These sutures exhibit excellent mechanical properties due to the exceptionally high tensile strength of small-diameter individual silk fibers. However, commercially available coated silk sutures do suffer from a number of drawbacks, most important of which include (1) the presence of tissue reactive impurities resulting from incomplete degumming of the raw silk yarn; (2) partial loss of tensile strength in wet biological environments due to hydration of the peptide linkages and silk macromolecules; and (3) high tissue reaction to naturally produced components present in major suture coatings, which are used to improve handling and knot tie-down properties. Extensive analysis of these drawbacks has been documented in U.S. Pat. No. 4,461,298 which was directed to composite sutures of multifilament silk embedded in a highly flexible, hydrophobic, highly deformable matrix made of a thermoplastic elastomer. The sutures were claimed to cause minimal irritation in living tissues and retain their strength in vivo for extended periods of time, while retaining the desirable handling qualities of silk. The sutures were prepared by treating commercially available, coated silk braids with a solution of a suitable polymer in a solvent and heating the moving suture through the solution to obtain a continuous impregnation of the silk with the elastomer. However, the polyester component in the specific combination of composite silk suture was a non-absorbable thermoplastic elastomer made of polyether soft segments and aromatic hard segments. Such polyester differs substantially from the absorbable polyesters of the present invention, wherein the polymers are made by the ring-opening polymerization of at least one cyclic monomer. More specifically, the polyester component of the '298 composite performs as a permanent barrier to the silk yarn, while the polyesters subject of this invention are used as a temporary shield or barrier only during the early period of implantation.
Although forms of the silk proteins have been investigated individually relative to their use in treating cancellous defects [Biomaterials, 26, 3527 (2005)], and as porous 3-D structures to support cell growth [Biomacromolecules, 6, 3100 (2005)] the prior art did not describe the use of silk multifilament in conjunction with synthetic absorbable polyesters as hybrid devices having two modes of degradation—silk degrades proteolytically, while the synthetic polyester degrades/absorbs hydrolytically. And this, in part, provided the incentive to pursue the present invention, which addresses silk/absorbable polyester hybrid devices such as braid silk sutures having an absorbable polyester coating made from at least one cyclic monomer.